1. Field of the Invention
This invention generally relates to an automobile antenna and, more particularly, to a rod-type automobile antenna provided with means for eliminating a whistling sound or noise generated during automobile driving operation and a method for manufacturing such an antenna.
2. Description of the Related Art
An antenna using a rod-shaped antenna element is most common for use with automobiles. An automobile antenna using such an antenna element generates a whistling sound or noise when the automobile runs at a high speed or when the non-running automobile is exposed to a strong wind. Such whistling sound is annoying to the occupants of the automobile. Various attempts have been made to eliminate the whistling sound. One attempt has been to streamline the cross section of the antenna element itself or a material covering the antenna element, to reduce its resistance to wind pressure and thereby to eliminate the whistling sound.
The process of streamlining the cross section of an antenna, however, is complex and costly. In addition, in order to reduce resistance to wind pressure at high efficiency, it has been necessary to precisely direct an apex of the streamlined cross-section towards the direction of the wind. The direction of wind blow, however, is not always constant so that directional adjustment has practically been next to impossible. This approach has resulted not only in difficulties in eliminating the whistling sound, but also, in the worst case, in an increase of the amount of the sound. For this reason, an automobile antenna having a streamlined cross section is not successfully used.
In recent years, the improved capabilities of automobiles have greatly reduced various noise generations and provided quiet surroundings w thin the automobile. This has caused noise generated by an antenna not to be ignorable. In particular, the popularity of automobile telephones has prompted the creation of a quiet atmosphere and the elimination of a source of noise generation is urgently needed. For the above reason, a technique associated with the elimination of a whistling sound of an antenna has again come to light.